`java_export` Publishing should have a means of promoting a snapshot

At current state `java_export` is already able to publish a snapshot of the target. However, there is a need to make it so that the snapshot itself promotable, to ease use in a CD system.

Start by tracing the java_export entry point that publishes snapshots and review how the resulting snapshot is represented. Define how a published snapshot can be promoted for use by a CD system, then verify the behavior against the repository's existing publishing workflow. The issue does not name specific files or tests.

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